1. Field of the Invention
The present invention is directed to an electromagnetic transducer for generating sound in hearing aids.
2. Description of the Prior Art
An electromagnetic transducer which serves the aforementioned purpose is known, for example, from I. Veit, Technische Akustik, Vogel Verlag, Wxc3xcrzburg, 1978, and has a housing containing an electromagnetic drive that is comprised of a coil, a drive magnet and an armature arrangement. A membrane arrangement that is mechanically coupled to the armature arrangement in order to convert movements of the armature arrangement into sound signals is secured in the housing.
This known electromagnetic transducer has only one armature and one membrane, so that the efficiency of the transducer is limited, and, moreover, the moving parts lead to vibrations of the overall transducer arrangement during operation of the transducer.
An object of present invention is to provide an electromagnetic transducer wherein the efficiency of the transducer arrangement is improved and feedback phenomena of the device caused by vibrations are avoided or at least diminished.
This object is achieved in accordance with the invention in a transducer of the type described above wherein the membrane arrangement is formed by two separate membranes that are arranged at opposite sides of the drive but are otherwise identically fashioned and are oppositely driven such that the overall mechanical pulse occurring due to the movement of the driven or driving parts is minimized.
The basis of the invention is to consistently implement two principles in the transducer arrangement, namely a highly symmetrical movement of the driving and driven parts and strictly opposed operation of the moving and moved parts such that the overall mechanical pulse occurring due to the movement of these parts is minimized. This results in vibrations being avoided, and thus feedback phenomena can be largely suppressed from the very outset.
In a preferred embodiment, the two membranes are symmetrically arranged relative to the drive. This is a consistent development of the symmetry concept.
In a further embodiment, an air space in communication with an output connecting piece of the housing is enclosed between the two membranes. Due to the opposite drive of the movement of the two membranes, a considerable improvement in the efficiency is achieved, so that an adequate performance of the transducer can be fundamentally achieved with smaller, i.e. less disruptive, movements of the driving and driven parts, which in turn assists in the reduction of the vibrations causing feedback.
In a further embodiment, the armature arrangement has two separately movable armatures. Each armature is connected to one of the membranes. This leads to a further symmetry of the overall structure and of the individual components. The two armatures can be identically fashioned and can be pre-mounted in conjunction with the two membranes.
In an embodiment of the invention two separate armatures are arranged between the respective poles of a drive magnet and the middle region of the membranes and proceed parallel to the membranes, at least in sections. The membranes are centrally connected to the armatures. Given excitation of the field coil, the armatures are either opposite attracted or repelled in common by the drive magnet, leading to an opposite but symmetrical movement of the membranes as well as of the drive parts.
In another embodiment the drive magnet arranged between the membranes is centrally divided, but the armatures are not arranged between the ends of the drive magnet and the membranes, but in the form of armature tongues, proceed parallel side-by-side in a center gap of the drive magnet. The connection of the armature tongues to the membranes ensues via a rigid connector element that is secured to the free end of each armature tongue. Both armature tongues merge via intermediate regions bent outwardly from their common plane into a U-shaped end region that is surrounded by a coil. The armature tongues, the middle regions and the U-shaped end region of the armature elements thus form a closed magnetic circuit, which leads to an especially advantageous compensation of the constant magnetic force given employment of the double membrane principle with two armatures.